This invention relates generally to radar systems, and more particularly, to a system and method for object detecting with a radar system.
Radar systems, and in particular, millimeter-wave pulsed Doppler radars are increasingly used for different applications. For example, these radars are increasingly used in automotive applications, including automotive sensor systems for cruise control, parking aid, stop and go control, pre-crash avoidance, etc. These radars also are used in other applications, for example, military and satellite tracking systems.
Known pulsed Doppler technology uses an amplitude sensing ratio (ASR) of the sum and difference patterns to determine target angle information. Essentially, the sum pattern and a delta pattern amplitude ratio are used to determine the target angle. This is also sometimes referred to as a switching lobe radar (SLR) system. The sum and delta patterns are typically obtained by signal combination and subtraction of two columns of an antenna array. The ASR value and a phase difference (PD) are determined based on the properties of the radar (sensor) and the target appearance angle toward the sensor. Accordingly, the characteristics of the ASR and PD are often used for target angle determination, where the ASR value is used to determine the absolute target angle and the PD value is used to determine whether the target is on the left or right side of the sensor (i.e., negative or positive angle with reference to the boresight of the sensor). A switch is used to change the phase difference between the two columns of the antenna arrays between zero degrees and 180 degrees and to maintain equal amplitude at the two antenna columns.
In general, a radiation lobe is typically defined as a portion of a radiation pattern bounded by regions of relatively weak radiation intensity. The main lobe is a high radiating energy region. Other lobes are typically called sidelobes and the lobe radiating in the counter direction to the desired radiation direction is typically called the back lobe. Regions for which the radiation is very weak are called nulls and the depth of the null defines how well the radiated signals cancel each other and, thus, can affect the performance of the system. The differential pattern for known radar systems often has a limited null depth resulting in reduced accuracy (e.g. angle resolution) of the detected target angle at the antenna boresight. In particular, the null location is at about the boresight of the sensor and any irregularities in this area directly affect the target angle detection accuracy. Accordingly, any small interference signal to the delta signal causes a large fluctuation of the ASR value, which may cause large ambiguity of the ASR value used by these known radar system for target detection. Thus, the antenna pattern of the sensor is very environment dependent resulting in ASR information used for target angle detection in known radar systems becoming inaccurate or possibly invalid. The reduced accuracy is even greater for smaller targets or targets located at a greater distance from the radar system because the SNR decreases due to the small reflection signal received.